2Meanwhile, melt 2 Tbsp. unsalted butter in a large heavy skillet over medium-high heat. Arrange one-quarter of 1½ lb. wild mushrooms (such as porcini, hen of the woods, chanterelle, or shiitake), sliced if large, halved or quartered if small, in an even layer in skillet and season with kosher salt. Cook, tossing often, until tender and beginning to brown, about 3 minutes; transfer to a medium bowl. Repeat process with remaining mushrooms, adding another 2 Tbsp. unsalted butter to skillet between batches.
3Melt remaining 1½ Tbsp. unsalted butter with 1 Tbsp. extra-virgin olive oil in a large heavy saucepan over medium-low heat. Add 1 large leek, white and pale green parts only, finely chopped (about ¾ cup), and season with salt. Cook, stirring often, until soft, about 4 minutes. Add 1¼ cups arborio rice, increase heat to medium, and cook, stirring often, until grains are translucent around the edges, about 3 minutes. Pour in ¼ cup dry vermouth and ¼ cup dry white wine and cook, stirring, until liquid is absorbed, about 1 minute. Add ¾ cup broth; cook, stirring often, until broth is almost completely absorbed, about 1 minute. Continue to add broth ¾-cupful at a time, stirring to incorporate and cooking until each addition is almost completely absorbed before adding more. Cook, stirring often, until rice is halfway cooked, 8–10 minutes. Stir mushrooms into risotto. Continue adding broth ¾-cupful at a time, stirring to incorporate and cooking until each addition is almost completely absorbed before adding more. Cook, stirring often, until rice is tender but still firm to the bite and risotto is creamy, 8–10 minutes. Stir in ¼ cup finely grated Parmesan (if using).
